The minority carrier diffusion length, LD, was directly measured in individual ZnO nanowires by a near-field scanning photocurrent microscopy technique. The diameter dependence of LD suggests a diameter-dependent surface electronic structure, particularly an increase in the density of mid-band-gap surface states with the decreasing diameter. This diameter dependence of the surface electronic structure might be a universal phenomenon in wurtzite-type nanostructures, and is critical in interpreting and understanding the effects of surfaces on various material properties.

1.
A.
Motayed
,
M.
Vaudin
,
A. V.
Davydov
,
J.
Melngailis
,
M. Q.
He
, and
S. N.
Mohammad
,
Appl. Phys. Lett.
90
,
043104
(
2007
).
2.
A. C.
Ford
,
J. C.
Ho
,
Y. L.
Chueh
,
Y. C.
Tseng
,
Z. Y.
Fan
,
J.
Guo
,
J.
Bokor
, and
A.
Javey
,
Nano Lett.
9
,
360
(
2009
).
3.
J. E.
Allen
,
E. R.
Hemesath
,
D. E.
Perea
,
J. L.
Lensch-Falk
,
Z. Y.
Li
,
F.
Yin
,
M. H.
Gass
,
P.
Wang
,
A. L.
Bleloch
,
R. E.
Palmer
, and
L. J.
Lauhon
,
Nat. Nanotechnol.
3
,
168
(
2008
).
4.
I.
Shalish
,
H.
Temkin
, and
V.
Narayanamurti
,
Phys. Rev. B
69
,
245401
(
2004
).
5.
Q. X.
Zhao
,
L. L.
Yang
,
M.
Willander
,
B. E.
Sernelius
, and
P. O.
Holtz
,
J. Appl. Phys.
104
,
073526
(
2008
).
6.
C. M.
Lieber
and
Z. L.
Wang
,
MRS Bull.
32
,
99
(
2007
).
7.
W.
Lu
and
C. M.
Lieber
,
Nature Mater.
6
,
841
(
2007
).
8.
R. X.
Yan
,
D.
Gargas
, and
P. D.
Yang
,
Nat. Photonics
3
,
569
(
2009
).
9.
A.
Soudi
,
E. H.
Khan
,
J. T.
Dickinson
, and
Y.
Gu
,
Nano Lett.
9
,
1844
(
2009
).
10.
A.
Soudi
,
R.
Lopez
,
R. D.
Dawson
, and
Y.
Gu
,
Appl. Phys. Lett.
95
,
193111
(
2009
).
11.
See supplementary material at http://dx.doi.org/10.1063/1.3456390 for current-voltage characteristics of ZnO nanowire Ohmic devices and Schottky diodes, schematic setup of the near-field SPCM, verification of the low-level injection condition, the model of LD as a function of nanowire diameter, and a discussion of obtained S and N.
12.
R.
Cuscó
,
E.
Alarcón-Lladó
,
J.
Ibáñez
,
L.
Artús
,
J.
Jiménez
,
B. G.
Wang
, and
M. J.
Callahan
,
Phys. Rev. B
75
,
165202
(
2007
).
13.
M. C.
Putnam
,
D. B.
Turner-Evans
,
M. D.
Kelzenberg
,
S. W.
Boettcher
,
N. S.
Lewis
, and
H. A.
Atwater
,
Appl. Phys. Lett.
95
,
163116
(
2009
).
14.
Y.
Gu
,
J. P.
Romankiewicz
,
J. K.
David
,
J. L.
Lensch
,
L. J.
Lauhon
,
E. S.
Kwak
, and
T. W.
Odom
,
J. Vac. Sci. Technol. B
24
,
2172
(
2006
).
15.
The photocurrent map appears to be “noisier” under forward-biased condition because of a large dark current, which required a lower sensitivity setting of the current amplifier.
16.
The localized band bending (or the space-charge region) associated with the Schottky contact can extend into the nanowire region under high reverse biases. However, the photocurrent spatial profile remains unchanged under various biases (not shown here), indicating that the hole transport is diffusion in nature.
17.
J. L.
Kann
,
T. D.
Milster
,
F. F.
Froehlich
,
R. W.
Ziolkowski
, and
J. B.
Judkins
,
J. Opt. Soc. Am. A
12
,
1677
(
1995
).
18.
This value is larger than the nominal NSOM aperture size (100–150 nm), probably due to the finite distance between the NSOM probe and nanowire surface (Ref. 17): the “wear and tear” of the NSOM probe during the scan might also be a factor.
19.
O.
Lopatiuk
,
L.
Chernyak
,
A.
Osinsky
,
J. Q.
Xie
, and
P. P.
Chow
,
Appl. Phys. Lett.
87
,
162103
(
2005
).
20.
Y. I.
Alivov
,
B.
Xiao
,
S.
Akarca-Biyikli
,
Q.
Fan
,
H.
Morkoc
,
D.
Johnstone
,
O.
Lopatiuk-Tirpak
,
L.
Chernyak
, and
W.
Litton
,
J. Phys.: Condens. Matter
20
,
085201
(
2008
).
21.
F.
Léonard
,
A. A.
Talin
,
B. S.
Swartzentruber
, and
S. T.
Picraux
,
Phys. Rev. Lett.
102
,
106805
(
2009
).
22.
D. K.
Schroder
,
Semiconductor Material and Device Characterization
, 2nd ed. (
Wiley
,
New York
,
1998
).
23.
If, alternatively, the surface states arise due to the presence of surface adsorbates, a diameter-independent surface electronic structure would lead to a constant S for different diameters, opposite to our observations. Therefore, the argument of a diameter-dependent surface electronic structure is still valid.
24.
P.
Schröer
,
P.
Krüger
, and
J.
Pollmann
,
Phys. Rev. B
49
,
17092
(
1994
).
25.
K.
Ozawa
,
K.
Sawada
,
Y.
Shirotori
,
K.
Edamoto
, and
M.
Nakatake
,
Phys. Rev. B
68
,
125417
(
2003
).
26.
N. L.
Marana
,
V. M.
Longo
,
E.
Longo
,
J. B. L.
Martins
, and
J. R.
Sambrano
,
J. Phys. Chem. A
112
,
8958
(
2008
).
27.
N.
Malkova
and
C. Z.
Ning
,
Phys. Rev. B
74
,
155308
(
2006
).

Supplementary Material

You do not currently have access to this content.